text:
Can "a drone" damage the wing of "an aeroplane" to the extent it actually threatens its ability to fly?
I stumbled across this video by the University of Dayton, showcasing the amount of damage a certain type of drone can do to a wing, and they wrote a whole article about it. While most of said article sounds like marketing for their research institute with very little actual information about the video they just released, the key thing to take away seems to be that:

researchers in UDRI’s Impact Physics group launched a 2.1-pound DJI Phantom 2 quadcopter at the wing of a Mooney M20 aircraft. The drone did not shatter on impact, but tore open the leading edge of the wing as it bore into the structure, damaging its main spar.
[...]
The researchers then fired a similarly weighted gel “bird” into a different part of the wing to compare results. “The bird did more apparent damage to the leading edge of the wing, but the Phantom penetrated deeper into the wing and damaged the main spar, which the bird did not do.”

If we trust that the researchers accounted for the fact that a damaged wing's structure is obviously compromised in places and that they also accounted for bones making an actual bird slightly more rigid than pure gel, as well as repeating the experiments often enough to make above statement with a reasonable degree of confidence -- none of which the article mentions explicitly -- then what conclusions can we draw from this?
It looks dramatic. Sounds dramatic, too, if you know nothing about aviation at all, which I guess was the intention when they wrote the article.
But how significant is the damage really?
The article doesn't say.
One YouTube comment by one "Stephen Mann", appearing to claim piloting experience states:

You can throw, at 200 MPH, anything weighing 2 pounds at a sheet of 2024-O .04" aluminum, typical of aircraft wings, and get this damage.  I've seen worse hail damage.

and notes that:

the Mooney wing uses a thinner aluminum (0.038") than an airliner (0.04 to 0.05").  This made the Mooney lighter and faster, which was a marketing design.
I've had more than a few bird strikes during landing (none during takeoff that I was aware of).  Some were Canadian geese that weigh 10-15 pounds.  There was never any damage to the aircraft beyond cleaning up the bird guts from the wing.

while generally playing down the significance of the test:

Typically, no aircraft below 400 ft., where most drones operate, will be flying that fast.  On final approach most airliners are flying between 130 to 160 knots, and by the time a landing aircraft is below 500 ft. the flaps and slats are deployed and the A/C is probably going 120 knots.  General aviation aircraft, like the Mooney in this video, are typically flying between 70-110 knots on final approach.  Even slower on takeoff.

I'm reluctant to accept information from YouTube comments at face value -- especially since it may be biased. But if true, this may just reduce the usefulness of the test significantly. And although I guess that's quite possible, I'd like to think they put some thoughts into these experiments before conducting them.
So where does that leave us?
Can "a drone" bring down "a plane" by crashing into it? Most likely, if we're talking about these big US military type drones like the RQ-4.
But can a "hobby drone" (for lack of a better word) like the one shown in the video by the University of Dayton seriously threaten the fly-ability of "the average plane" (if such a thing exists)?
Or let's say we start at the Mooney and scale the damage up for larger planes. Would a plane with that kind of damage get into trouble whatsoever or would it just require a probably costly repair?

What happens if the hobby drone hits a windshield at 70 mph?

The drone opened the wing up in exactly the location where Pipers and Beech products store fuel (anywhere from 20-40gal on a single).  The combination of air, fuel, and spark from either the drone's electronics or broken wires in the plane itself could start a fire or create an explosion.  In practice, the pilot will likely attempt an evasive maneuver upping the stresses on the skin and structure.  The pressure change in the wing and added stress from maneuvering could pop lines of rivets that cause a structural failure.  Just spit-balling, but both of these seem realistic to me.

Wow, the drone just disappeared right into the wing.  That could interfere with aileron cables, flap cables, perhaps even the wet wings (sealed rib/skin areas on Mooneys  and Cardinals) and who know what to wiring that goes out to the wingtip strobe lights, navigation lights, wing mounted landing lights, and electric flap motor wiring. And if the drone batteries got damaged, who knows what the results could be.

This is what it looks like when a bird hits the window, that guy was lucky the bird didn't hit him in the face, a drone however would have turned into shrapnel...

Mr Mann doesn't have a clue what he's talking about.
Wings aren't made from 2024-O aluminum, which is fully annealed and very soft.  The usual heat treat state is T3 through T6.
A Mooney would NOT have .040" wing skins.  The skins will be .016, .020, .025 and maybe .032 in high stress areas around the wing roots. Leading edges would be .025 or maybe .032 inboard, and likely .020 or .016 near the tips and on the control surfaces.  Skin sizes are for structural efficiency and rigidity for minimum weight, not "marketing"... geez.
His approach speed comments are more or less correct, but a Canada Goose will do significant damage to any aircraft it hits in flight and has a good chance of bringing down a Mooney at any contact point.  A Mooney running into a goose at the wing will, at minimum, completely crunch the leading edge in back to the main spar.  A goose will do significant damage to the slat or leading edge of any airliner.  There was a CRJ900 that hit a goose size bird just below the windshield on the takeoff roll near V1, and it came back into the pilot's instrument panel, distributing guts and feathers all over the place.
Geese are bad news and are a vexing problem in the spring in central North America.  The terrain is all browns and if you are descending with a flock below and in front they are nearly invisible until you are passing through their level.
A goose hitting the windshield in front of the pilot or horizontal tail of a Mooney or similar light aircraft will probably bring it down.  On the wing, maybe.
A 2lb drone will do obvious damage as the test showed but would not bring down a Mooney unless it hit the windshield, incapacitating the pilot.  It would certainly go though a windshield.  1/8" plexiglass has roughly the same tensile strength as .020" 2024T3.   You wouldn't want to hit anything heavier than a few ounces with 1/8" of acrylic in front of your face as the only barrier.
So from that standpoint, drones of any size can be considered a hazard to aircraft.

According to https://wildlife.faa.gov/databaseSearch.aspx bird strikes in NY and NJ in March 2018 caused minor damage to one aircraft and no damage to ten others. Perhaps the risk is not as high as you are suggesting.

@ Paul Smith the vast majority of bird strikes are small birds hitting leading edges and going through engines of transport aircraft. They do little damage.  If you were paying attention, most of the strikes are small birds and a couple of ducks hitting transport/corporate airplanes.  I was talking about geese in the case of airliners, and on light aircraft, just about anything bigger than a chickadee hitting the windshield in front of your face will become unpleasant.  That being said, bird strikes on light aircraft are quite rare, mainly because birds make an effort to get out of the way.

I certainly thought I had paid attention when I gave a verifiable reference for all bird strikes, small and large. What makes you think otherwise?

It's the size of the birds.  When I look it up I see robin, robin, robin, gull, gull, kestrel, yadda yadda yadda.  Couple of ducks.  No geese.   A robin hitting an airliner leading edge is like a large bug to a light aircraft.  As  I mentioned, birds generally get out of the way of slow moving GA aircraft and strikes are quite rare.  Drones don't get out of the way and are a bigger potential hazard to light aircraft in my opinion.  A 2lb drone coming through the windshield of a C-152 will ruin someone's day.

What is your fascination with geese? Of the 13 reported bird strikes in NJ in March 2018, none were geese. 7 were birds that are typically over 2lbs (the size of the drone in question) and the damage reported by these strikes was none. Zero, zilch, nada. Is there a risk, yes. Is it significant? On the evidence, no.

Well that's what I said.  If you read the original post, the Mann dude talks about hitting geese which don't do much damage.  My point is small birds on large aircraft, not too big a deal, but geese are another story and are the biggest hazard to large aircraft and the Mann dude is full of it.  Light aircraft rarely run into birds at all because they are noisy and move slowly enough for the bird to evade.  A drone will not evade however, and would be a bigger hazard than a bird to a light airplane.

To @JohnK, I am not an aviation person so am not doubting your expertise.  However, I find it odd, based on your above answer, that any plane would be allowed to fly with a "1/8" plexiglass" windshield.  I would expect (as an outsider to the aviation industry) that the FAA (or suitable governing body) would require at least something more substantial and shatter-resistant than just plain plexiglass for any aircraft windows, whether front or side, no matter whether it's for commercial, or GA use.

A 1/8 plexi windshield is actually quite strong.  Cast acrylic used for airplanes is 10ksi vs 40ksi (yield) for 2024 alum.  A 1/8" sheet of plexi has about the same tensile strength as an .032" aluminum skin.  Most light plane skins are .025 or .016".  Although the plexi is not very ductile and tends to shatter rather than bend, a bird would go a panel of aluminum that makes a typical aircraft skin just about as easily.  Airliner side windows are generally 1/4 inch, and have roughly the same strength as the adjoining skin structure.  You won't see 1/4 plexi used anywhere in GA airplanes.

One of my uncles has had various positions with the FAA over the past decade, and he came home for Christmas at one point with pictures of a plane that had taken a bird through the windshield...  Specifically a Turkey Vulture...  Which had a full stomach at the time...  The physical damage was impressive, but reportedly the stench was what made attempts at repairs close to impossible.

Like anything in aviation it depends.
A drone could easily severely damage any fabric-covered wing. This is everything from ultralights up through piper cubs and lots of high-powered backcountry fliers. Losing your wing covering can be a big issue at speed but whether or not the damage brings the plane down depends on where and how it hits as well as the pilot's response to the incident.
Metal-covered wings are a bit of a different story and it really depends on the airframe. In some cases, you can shear a whole wing off and be fine or even lose a huge chunk of your fuselage while with others airframes small damage can cause serious handling issues and potentially lead to an incident. Spoiled airflow would be the ultimate issue with leading edge damage from the video but this does not mean a crash necessarily. There are even instances where deliberately spoiling the airflow is called for.
If you watch the video closely you can also see that the drone impacts directly next to a wing rib which is a weaker area than if the drone impacted a rib itself. I would be curious to see a test impact on a rib collision as well.
Ultimately it may be more of an issue of where then if (similar to this question). As noted in the comments by various people you run the risk of puncturing a fuel tank, damaging or otherwise jamming control cables, and even damaging the spar all conditions that can potentially lead to an accident but it's highly situationally dependent.
It's also worth noting that GA planes generally have fairly weak leading edges (as you can see in the video). Larger transport aircraft may have things like leading edge slats or de-ice systems that make the wing leading edge a bit stronger by design.
Just to nit-pick the semantics a bit, they list the fact they used a Mooney M20 aircraft, strictly speaking, the M20 spans from the wood wing A variant all the way up through the current TN/S variant the wings vary heavily in design even within that family of aircraft. They are clearly using a metal wing, likely of a newer airframe but you can see how even that could change the outcome of the collision.

or would it just require a probably costly repair?

All aviation repairs are costly...


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Why does the FAA mandate a temperature indicator for all manned balloons?
14CFR31.85 ("Required Basic Equipment" for manned free-air balloons) requires an Envelope Temperature Indicator (ETI). This is a requirement of the FAA, not necessarily the manufacturer. Some balloon Flight Manuals do not even mention an ETI.
My question is, is there somewhere that explains why the FAA mandated a ETI for all hot air balloons, and how it's used with regard to the determination of load, overheating and gross lift with a hot-air balloon? (Might be more than one question! ;-))
There does not seem to be an industry standard, and the temperature inside a HAB is critical to flight performance and safety.
Best regards,
FFG

Welcome to Av.SE

"and the temperature inside a HAB is critical to flight performance and safety" - Might that possibly be why the FAA mandates an ETI?

Is it to do with ice forming on the envelope?

the balloon handbook which you should be keeping in your balloon, has a chart that shows lift/payload based on ambient and internal temp at the sensor.  plus your log book shows the weight of the equipment, and in flight school you learned the weight of propane, so you can easily compute the spare payload you have to carry for the temp shown in the weather report plus the max you want or can run the envelope safely.  thats how you use it with regard to determination of load

the sensor is critical to safety as well as flight operations.  idealy you shouldnt hit max temp or be close to it.  at the same time you dont carry a scale and weigh each passenger, but before launching you do check for equalibrium and can check the temp then which is the same as weighing everything, flight time will be hotter than that but with experience you get a feel for how close to the margin you are

if you fly hot habitually you will wear out the fabric quickly and the overall life of the envelope can be short.

A hot air balloon (including the air in the envelope) has tremendous mass, so it takes a long time for a change in buoyancy to cause a change in vertical speed.  Watching for temperature changes on the Envelope Temperature Indicator will help a pilot anticipate changes in the balloon's vertical speed before they have actually had time to occur.
From page 7-4 of the FAA's Balloon Flying Handbook:

"Ascents and Descents
The temperature of the air inside the envelope controls balloon
  altitude. A balloon that is neither ascending nor descending is in
  equilibrium. To cause the balloon to ascend, increase the temperature
  of the air inside the envelope. If the temperature is increased just a
  little, the balloon seeks an altitude only a little higher and/or
  climb at a very slow rate. If the temperature is increased
  significantly, the balloon seeks a much higher altitude and/or climbs
  faster. If the balloon is allowed to cool or hot air is vented, the
  balloon descends.
Even without the input action by the pilot, it must be remembered that
  the air inside the envelope is dynamic. The air mass is constantly
  moving within the confines of the envelope, attempting to seek a level
  of equalization. While it varies with each envelope, input action by
  the balloon pilot can take from 6 to 15 seconds to be realized as a
  reaction by the balloon. Planning the maneuver, anticipating the
  reaction time, inputting the proper burn, and observing the reaction
  must result in smooth and natural movement by the pilot."

Also, as another related answer has noted, under some conditions it is possible for a pilot to bring the envelope to an unsafe temperature by excessive operation of the burner.  Monitoring the Envelope Temperature Indicator allows this to be avoided.  For a given desired maximum envelope temperature, the outside air temperature determines the total gross lift that is available at any given density altitude, or the density altitude that can be reached with a given gross weight.  See the FAA's Balloon Flying Handbook for more.

I know nothing about balloons but the FAA's Balloon Flying Handbook mentions at least two reasons.
First, it can be a limitation from the manufacturer:

Limitations. Restrictions placed on a balloon by its manufacturer. Examples are maximum envelope temperature and maximum gross weight

I don't know exactly why the limitation would be there, but I assume it's a material safety issue at some point.
Second, it's used for performance calculations to determine lift. The Handbook has a diagram on p. 3-9 and the explanation says:

Using the chart in Figure 3-13, determine the maximum gross lift that
  may be expected on a 60 °F day, with decisions not to exceed 190 °F
  envelope temperature and 1,500 feet pressure altitude. In this
  example, the established parameters equate what many pilots consider
  when doing performance planning. They decide they do not want to
  exceed a given altitude or envelope temperature.) To determine the
  maximum gross lift available, the nomograph should be entered at point
  A, at the ambient temperature of 60 °F. Move right, to the line
  indicating an envelope temperature of 190 °F (point B). Then, move
  down vertically to a point equidistant between the lines denoting
  altitude of 1,000 and 2,000 feet (point C). Then, move horizontally to
  the left to the gross lift axis of the chart and read the result
  (point D). In the illustrated example, this computation results in a
  maximum gross lift of 1,120 pounds.

source: Stack Exchange

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Would more throttle when using reverse thrust reduce stopping distance?
If more throttle is applied after engaging the reverse thrust, would it shorten the braking distance?

depends on the aircraft and the engine.

Broadly speaking, yes.
The standard method of operating reverse thrust on jet aircraft is to use the reverser levers, which are actually thrust levers as well.  As you pull the reverser levers up, you increase engine thrust.  Many aircraft types will have prohibited areas between idle reverse and full reverse thrust which should be avoided (for things such as blade flutter).  Importantly, reverse thrust is not considered when evaluating aircraft landing performance - it largely used to reduce wear and tear on the aircraft for reasons of economy of operation, usually idle reverse thrust is ample for this purpose.   As you suggest, in an emergency full reverse thrust can be used to reduce or prevent a runway overrun.
With propeller aircraft, turbine or piston, you may enter the 'beta' mode (if equipped), creating reverse thrust and selecting appropriate engine power as desired, though as with jets, there may also be prohibited engine speeds which may be passed through on the way to a higher speed, but not left at that level.

It's a bit of semantic nit picking, but on 747-100/200 aircraft, pulling the reverse levers up deploys the reversers. Then once they're up, pulling them back increases engine thrust. They won't come up unless the thrust levers are in the idle position and the aircraft is sensed to be on the ground.

Thanks Cpt Terry.  Indeed, all reversers I know of won't allow the reversers up until the thrust levers are at idle and other conditions are met.   This doesn't always include being on the ground, but that's uncommon.  I investigated airborne reverser deployments on a type intended to prevent airborne deployment.  In this type, a landing bounce could arm and initiate lift dumper deployment and the bounce of the pilot flying could also result in an un-intended reverser deployment.  The combination giving a hard landing indeed, but not quite enough to bend the aeroplane in the cases I looked at.

@PaulSaccani Indeed "uncommanded selection of reverse thrust" is an certification issue, and this is why: https://en.wikipedia.org/wiki/Lauda_Air_Flight_004. (The flight crew decided a warning was "just an advisory thing" and took no action - followed by their last recorded words "Oh, the reverser's deployed")

It's also common just to deploy reversers on landing without adding power, just to have them available if needed, while reducing FOD risk.  Some operators may discourage this because it uses up a reverser operating cycle without any brake wear and tear benefit and tell pilots to either use them or don't.

@alephzero A reverser deployed mid-flight is arguably unrecoverable.  It puts so much stress on the plane and is such an anomaly that people say the simulators are not accurate.  It is actually so dangerous that the FAA have mandated systems to prevent such things from happening mid-flight.

What FAR would that be?  As far as I am aware, there is nothing in the regs to prevent you certifying an aircraft for inflight use of reversers.  Preventing inadvertent reverser deployment is a different issue altogether, protections against that have been increased.  It is technically more complex and increases test requirements to operate them in flight, and some types are ill suited to it, so few aircraft have been certified for inflight reverser use.  For commercial reasons.

Tu-154 has a strong ground effect, reverse thrust can get it to touch down: https://www.youtube.com/watch?v=Yq5HLtdGeqE

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What happen if an aircraft is more than 10 hours overdue for its 100-hour inspection?
Let's assume an aircraft for hire's 100-hour inspection is about 20 hrs past due (120 hrs since the last 100-hour inspection). Can I just say that the aircraft is not airworthy and the aircraft cannot be operated?
Or, if I'm the owner, can I operate it just for personal flights? Is this illegal?

I'm assuming this is the US? What does "and another inspection have been done" mean?

Yes, in US. I mean AAVIATE.

FAR 91.409(b) says:

Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection and been approved for return to service ...

(Emphasis mine)
According to a literal reading of the regulation, it only applies to operation "for hire" and not to the owner(s) flying it for personal use. So, in theory, what you propose is legal.
However, if an FAA inspector ever reviews the log books and sees that you went over 100 hours between successive 100-hour inspections, you would need to provide evidence that every such flight was not for hire, which could cost you significant time and effort.
So, while it is technically legal, in practice it is unwise. If the plane is regularly used for hire, get it inspected every 100 hours regardless of the nature of specific flights.

No this regulation says nothing about what is required when the operation is not for hire. Your summary is akin to reading that "assaulting a police officer is a crime" and concluding that assaulting anyone who is not a police officer is legal.

@Hugh That's the way regs are written. They are restrictive rather than permissive. If the regs are silent on a subject then it is allowed. It may be restricted by a different regulation, but I don't think the 100-hour rule is anywhere else.

@Hugh That is exactly how laws work. See Everything which is not forbidden is allowed and Nulla poena sine lege.


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Why, on carrier landings, does the Flight Path Marker (FPM) seem to be placed near to the end of the runway?
On most military aircraft landings, the FPM seems to be usually lined up with the start of the runway, either around the numbers or the aiming point, I would asume this to be the same on carriers for a higher probability of catching the wires, But it seems in most videos, the FPM is placed almost off the end of the runway.
Ex:

 (Loud noise)

Seems to be answered here: What makes it so hard to land on an aircraft carrier?

Flight path marker @CatchAsCatchCan

Ahh okay, so its due to the carriers forward movement? @fooot

The short answer is that it is because the carrier is moving toward the point that the FPM is indicating; where the ship and aircraft will converge at the moment of landing.
In reviewing my answer to the other question linked in the comments, it struck me that some clarification might be needed to distinguish between landing visually, or by reference to ship based ILS, versus flying a HUD equipped aircraft.  In the first two cases, (visual or ILS) the frame of reference is the ship itself.  Whether the ship is stationary with 30 knots or natural wind across the deck, or steaming at 30 knots to make wind on a calm day, the indications to the pilot are identical.
Contrast that with a HUD equipped aircraft.  The FPM uses the earth as a frame of reference, not the ship.  It shows where the aircraft is going relative to the surface of the sea, its position is based on calculations from inputs of GPS and air data computer, and factors in the wind.  (which itself is calculated…)  It doesn't know or care if the ship you are trying to land on is moving.  Therefore, if the ship is stationary one would expect that the FPM would indicate a touchdown point right in the landing area.  Just as it would a stationary runway on land.  (if the pilot is doing his or her part!)
If the ship is steaming at 30 knots the FPM will still indicate where the aircraft is going relative to the surface of the sea.  However, since the carrier is moving as well, the FPM will be out in front and to the right of the landing area during approach.  (Because the ship hasn’t gotten there yet!)
In the video you can see that the ship has a decent wake behind it, but as the aircraft closes in the FPM moves from up and right, to right in the landing area at touchdown.
Keep in mind also that the FPM is pretty much instantaneous, so that pilot corrections to glideslope deviations will show up as well.  For example, if the pilot rolls out high and right at the start, even if the ship is making all its wind the proper correction might put the FPM down and left until re-correcting.
And finally, the Navy discourages “HUD Cripples”.  While (I have heard) it is a wonderful tool, the pilot should reference the traditional meatball, lineup, and AOA on short final.  So while the pilot is supposed to be aiming for the ship, his or her FPM may actually be aiming just a bit in front!  ;)


text:
What aircraft is this and to which air force does it belong?

Hi, could someone identify the type of this fighter jet and the air force which operates it? Thanks!

Panavia Tornado, Royal Air Force (UK), 13 Squadron.
The aircraft in the question is identified as belonging to No. 13 Squadron by the distinctive green, yellow and black 'Squadron flash' painted on the aircraft side  below the front part of the cockpit.

Royal Air Force roundel

13 Squadron flash

Above: a Tornado of No. 13 Squadron as seen at the 2007 CIAF air show in the Czech Republic. The squadron flew Tornado GR.1A aircraft from 1990, and later the GR.4 and GR.4A variants.
Here is ZA401 (a GR.4) at RAF Leuchars in 2005 with the 13 Sqn flash painted on the tail as well as the normal place, as part of the Squadron's 90th anniversary celebrations:

No. 13 Squadron RAF (Wikipedia)

Many squadrons have used this plane (9, 14, 15, 16, 17, 20, 27, 31, 45, 75, 617), but are you sure about 13? It seems to be one of the few that hasn’t?

@Tim - 13 Sqn operated Tornados from 1990 to 2011, first from Honington and then in 1994 moved to Marham.

I never liked them much when they were in service, but now they are gone, I feel a bit nostalgic about Tornados. I think ZA401 looks nice above.

ahh so they did. Strange the page on the Tornado misses that off. I wonder if it’s because of the disbanding / reformation

That is a Panavia Tornado operated by the UK Royal Air Force.

You can tell by the shape of the nose wheel door, and the rear of it has a characteristic boxy shape with the stabilators lower than the wing. The roundel is the RAF low visibility roundel.

The shape of the nose is characteristic.

@MichaelHarvey characteristic of the Tornado IDS, bomber-striker, while the Tornado ADV interceptor had a longer nose.

@MichaelHarvey why is it’s nose so pointy? It’ll poke somebody’s eye out!

You can also narrow it down by being twin-engine and flown by the RAF.  The other twin-engine options are the Canberra, Lightning, Buccaneer or Typhoon, all of which have very distinctive shapes which this clearly is not.


text:
Solar biplane possibilty?
The solar impulse has a massive wing span, greater than a jumbo jets. Would it not be possible to have a biplane design to shorten the wingspan(making it more practical and maneuverable)and have the wings offset so that they both capture the sun?

But wingspan is good. They need great wingspan.

Not very practical though for future transport. The drag produced from a biplane design would not be a big factor due to the slow speed of a solar plane.

The drag produced from a biplane design would be a huge factor, because it is the short span that causes the drag, especially at low speed.

Wouldn't it make more sense to increase wing chord? This way you only have one boundary layer (= less drag) and a much thicker wing. Makes you wonder why the designers of the Solar Impulse didn't choose to do so, doesn't it?

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text:
How does the performance of an aircrafts propeller change with respect to distance from obstructions?
I am interested to know if there are any changes in propeller performance (thrust, efficiency) with respect to distance from obstructions such as the fuselage or wings?
I am particularly looking for studies or experiments. Mostly interested in tractor/puller configurations but info for pushers would be nice to know too.

Welcome Stephen! Some elements of the answer here: What are the factors considered while placing a propeller on a plane? (and also the linked question) -- and --- Differences in aircraft performance between tractor and pusher propeller designs?

A propeller accelerates air, and the stream tube going through the propeller disc can be idealized as something which is initially wider than the propeller disc and contracts while being accelerated (Froude's propeller hypothesis). Now two types of obstruction are possible:

Obstructions to the flow near the propeller axis, and
Obstructions to the flow near the stream tube.

It is quite obvious that something which blocks the flow will reduce the propeller's efficiency, and since flow speed is higher behind the propeller, the same obstruction will reduce performance more if placed behind the propeller disc. This is why pusher designs show better performance with the same engine power.
But also objects near the outer edge of the propeller can reduce efficiency. When a wall on one side ahead of the propeller prevents air from flowing towards the disc, the flow though the propeller disc is disturbed and efficiency will suffer. Similarly, a wall past the propeller will prevent a symmetric outflow, and the stream tube will attach to the wall (Coanda effect). This can be used to the advantage of high lift devices on wings, but will generally reduce efficiency.
For experimental data, I recommend to read NACA reports like the one for engine cowling development or this one on fuselage-propeller interference.

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text:
Is it still "landing" in a seaplane?
This probably sounds like a silly question, but I was watching floatplanes land on Lake Union, Seattle, and it got me wondering whether a plane that touches down onto water is still talked about as "landing" in aviation parlance.
Is it?

To be fair, you (the pilot) do end up on land eventually...  Well, unless you're flying an MVP.Aero, then maybe not...

Well sure, but you don't call driving home "bedding" since you end up in bed at the end of the day.

It's a watering.

I think if you said "watering" you'd get some funny looks and/or some good laughs.

I propose "Splashdown"

Added a tag USA, as in my language there are two distinct words, and using landing on water would be very fun.

You park on a driveway and you drive on a parkway. Isn't English weird?

Also, you can carry cargo by ships and shipment by cars.

I'm not sure [USA] is appropriate, [English], maybe, but I don't see any Canadians or Brits chiming in with non-AmE answers.

@JanDvorak "Get on the plane? F*** you. I'm getting IN the plane." -George Carlin

Is it any more odd than "sailing" a ship powered by steam or diesel instead of sails?

Yes. One 'official' example is from the FAA's test standards for land and seaplanes, which includes these tasks for seaplanes:

Task H: Glassy Water Approach and Landing
  [...]
  Task J: Rough Water
  Approach and Landing

The FAA's Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Handbook also uses it; Chapter 6 is called "Seaplane Operations - Landings".
Interestingly, the word "landing" itself isn't defined in the FAA's glossary or in 14 CFR 1.1 (the US air regulations general definitions). Presumably it's considered to be too 'obvious' to require a definition.

Haha, related to the landing definition: Can a “crash landing” be used for FAR 61.57 currency?

In more logical languages than English, no. In German it is "wassern" while landing on land is "landen".

@PeterKämpf Yes, Spanish is another one: aterrizar vs. amerizar.

English doesn't stand alone though. Dutch also doesn't have a specific word for it and merely calls it a "landing" (or "noodlanding" for "emergency landing", which still isn't limited to water). And in German, while as mentioned the word wassern/Wasserung does exist, the use of the more general word landen/Landung would not be wrong, a Wasserung is a specific type of Landung.

So, you land a seaplane to get from air to water, and then you land it again when you sail it to a dock?

... then you land it the third time when you pull it onto a truck and drive it to its owner?

Not in French it isn't. French for landing is 'aterrir' which roughly translates to 'return to the land'. Using this verb for a sea 'landing' would sound silly to them so they use 'amerrir' which means 'return to the sea' (Mer being French for sea, terre is French for ground). A landing in the Moon would be 'alunir'.
This interesting fact was mentioned by the instructor on my French audio course.

A landing on any planet or satellite, or on an asteroid, will still be un atterrissage (a landing), as atterrir (to land) is not returning to Earth (la Terre), but to the ground (le sol). The neologisms alunissage and alunir (Moon landing, to land on the Moon), which are frequently used, have been in fact rejected by the Académie française. That matches with English use, as in the Eagle has landed (Apollo 11).

No. ICAO defines a landing like this:

From the beginning of the landing flare until aircraft exits the landing runway, comes to a stop on the runway, or when power is applied for takeoff in the case of a touch-and-go landing.

(source)
And a runway like this:

A defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft

(source)
Wikipedia suggests that "landing" on water is referred to as "alighting"

Does ICAO define "alighting"?

Not as far as I can tell. However, the following document contains this definition: "water alighting area: means a suitable stretch of water for the landing or taking-off   of   a   float   plane   under   specific conditions" - http://www.icao.int/APAC/Meetings/2016%20WASWG2/!IP%2001%20-%20Water%20aerodromes%20requirements.pdf

Haha, by definition they exclude "landing" on water, but then specifically refer to landing when talking about what a float plane does on water?  Classic!

Indeed hehe .. not very well thought through

So what is it called when you deliberately and controlledly put an airplane on solid ground after a flight in the same way that you would land, but you don't do it on a runway?


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Is it acceptable to use VNAV data in lieu of localizer recommended altitudes?
My airline's vertical navigation data isn't certified for use and is considered 'advisory' only.  But, 90% of the time it provides highly accurate data.
Some instructors at my company contend that 'localizer recommended altitudes' are required to be used as the primary / only reference for a CANPA style continuous descent to our DDA (derived decision altitude) on localizer approaches.
I contend that any method chosen for a descent to DDA is purely technique and as long as our advisory VNAV data is backed up with other data & looks accurate, there's nothing wrong with using it.
Are localizer recommended altitudes regulatory in any way?  Is it legal to use an 'advisory' Vnav data to fine-tune your descent from the FAF to DDA? Any links, references, or regulations you can point me to on the subject would also be greatly appreciated.

If you want to be pointed to regulations, please include which jurisdiction you are operating in (e.g. the tag faa-regulations)

You might get a better response to this question if you not only add the jurisdiction (FAA?) but also post a specific approach plate that shows exactly what your question is about.

If your company uses CANPA (continuous descent) approaches, the whole point is using artificial VNAV on non-precision approaches where no vertical navigation is part of the approach. This involves determining a DDA, or derived decision altitude, based on the published minimums and some other criteria. Arrival at the DDA requires a go-around just like if you were arriving at a DA on a precision approach.
In defense of your point, if you aren't using any form of vertical navigation, one might argue that it's no longer a CANPA approach at all. How can be maintain a constant angle without vertical nav?
Then again, if you are flying the CRJ a localizer approach would involve having the Proline 4 in "green needles." Advisory VNAV only works in "white needles," so if they're saying you shouldn't use advisory VNAV on a localizer only approach that might be the reason. You can't.
In reference to the main question in the title, you can't use advisory VNAV "in lieu" of the published minimums or minimums derived from your company regulations, but if you want to use advisory VNAV to plan your descent to the appropriate minimums, that's okay unless specific language in the company manuals forbids it.


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What are some good resources on Jet Design?
I'm a student in high school, so please imagine you're talking to a toddler first, and second where would you advise I look for good documentation and guidance in jet engine design and tools to familiarize with.

Not me, but I knew several mechanical engineering students at university who did a (simplified) jet engine design project as part of their bachelor's degrees. Purely a paper exercise of course; but it involved such things as designing blade profiles and various aspects of mechanical design. So I'd suggest searching for course work and text books aimed at undergraduate university students at first.

The book (Turns, 2006) that came with a Thermodynamics course I took, contains a nice chapter on jet engines. I guess a single book like that will easily keep you entertained for a few months, equally so for each different aspect as mentioned by @Andy.

If this question were reworded a bit to be more like this one, or this one, it would be a better question. The format of this site is a bit better for "what are good resources" than "where did you learn".

Actually, my book suggestion got me thinking: why don't you just contact the nearest university that has an aerospace engineering faculty, and ask them which course books they use in their first year; they will probably be readily available second-hand near you.

That one depends on a lot of things.  Real jet engine design is going to require an understanding of advanced physics, computational fluid dynamics, thermodynamics, heat transfer, and metallurgy.  It will also require college level engineering coursework as well as at least calculus and in some cases partial differential equations on order to properly design such an artifact.
Not to be deterred, amateur jet engine builders have constructed self sustaining gas turbines using old turbochargers and a custom built isobaric combustion chamber as this YouTube video shows.  Both the reactive thrust and/or mechanical power one can get out of such a device is limited.
There are some existing plans available on the market for building small jet engines as this Instructables shows.
RC Aircraft modellers can also buy small scale turbine engines for around \$3,000-$5,000, depending on manufacturer, type, thrust output, etc.
Designing a proper jet engine from scratch is going to be much more difficult, though it is possible. It will be expensive and time consuming, but if you really want to learn the art of building turbine engines, it's possible.  I would advise waiting until college and pursuing a degree in aerospace engineering. The major aero schools (e.g. Michigan, Purdue, MIT, CalTech, etc. all have extra curricular clubs as well as design and testing facilities and equipment for this sort of stuff and as I said before you will need higher level engineering and mathematics education in order to do it right.  That's not to say this is impossible; the Rocket Boys, a pack of coal miner's sons whom the film October Sky was based upon, were designing Di Laval nozzles using differential equations in high school, so if you really want to learn, it's always possible, though not always easy.
If you do want to start down that path and want a challenge, I'd recommend The Design of High Efficiency Turbomachinery and Gas Turbines by Wilson and Korakianitis.  I'd also recommend primers on thermodynamics and heat transfer as well.
You might attempt the earlier turbocharger projects first or disassemble an RC jet engine to get a much better familiarization first, then attempt the engineering of an engine from scratch.
In addition, seek out other jet engine builders and talk with them.  They will be a wealth of information for you at the beginning of the project.
You might also seek out professors at a good aerospace engineering program somewhere and ask them what direction they would recommend you to begin such a project.  Remember: Old people find nothing more flattering than a youngster who will sit patiently and listen to what they do for a living; employ that to your advantage.
A long shot but it might work as well - get involved with Linkedin and look for profiles of engineers who are employed at places like UTC/Pratt & Whitney, GE Aircraft Engines, Rolls Royce, Eurojet, etc.  You might just find someone there who designs jet engine parts for a living and can be a good resource.
Also, as with any kind of engineering or programming, start simple and work up to complex.  Your not just building an artifact, you're building a database of knowledge of how to build such an artifact as well, which can be built upon in increasingly more complex designs.
Oh, and one final caution: gas turbines belch large, noisy quantities of high temperature, high pressure gas and operate at very high temps, creating the possibility of serious injury, explosions and/or fire hazards.  Approach the design and testing process with caution and take appropriate safety measures i.e. don't test this thing in your parent's basement, etc.


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How do pilots foresee turbulence?
During a normal flight at cruise speed and altitude, amid the delicious airline meal and the enjoying a latest movie, all of a sudden the seat belt sign turns on.
Then a few seconds later we enter turbulence, grab a hold of that half-finished soda cup and wait patiently for the bumps to be over while looking out the window.
So, how exactly do the pilots know that the airplane is about to enter in an air pocket which will cause turbulence?
... or does it happen like this?

I have already gone through the excellent answers here and here.

There are a few ways that pilots are aware of potentially turbulent areas.
Eyesight
The most obvious way is just by looking outside and observing the sky.  Large billowing clouds, called cumulus clouds, indicated pockets of unstable air (the clouds are rising because the air under them is as well).  If the pilots must fly through these clouds then its a safe bet that there will be some turbulence.
Weather Radar
Just like using your eyes, except the radar can see further through haze and other clouds.  Typically this is useful for finding embedded thunderstorms, but it can also be useful to find areas of potential turbulence.
Communication
Pilots talk.  Both to each other and to air traffic controllers.  En route controllers frequently ask pilots for "PIREPS" (pilot reports), to build an accurate picture of the flight conditions at different altitudes.  Often commercial aircraft will request to change altitudes or deviate around weather/ turbulence, so it is in the best interest of the controller to know ahead of time where the bad flight conditions are, and have a game plan of how to route traffic.  This makes it much easier for the controller to route traffic, rather than getting request after request from individual aircraft.

All very true, however, at cruise altitude (of jets) most turbulence would be caused by clear air turbulence (CAT). CAT is largely invisible to eyesight and weather radar, so pilots would depend on communication to avoid it as much as possible.

@Ben: Thunderstorms usually do reach all the way to jet cruise levels and are responsible for significant portion of turbulence there. But yes, clear air turbulence is significant and not detectable in advance. Sometimes it can be predicted, i.e. when you know where the jet stream is.

@JanHudec I'm not sure I've ever seen a pilot actually fly through a thunderstorm. Does anyone actually do that? They have to fly near them at times and that can be turbulent, but I was under the impression that actually flying through a Cumulonimbus cloud was generally considered to be something to be avoided to the maximum extent possible.

@reirab I can confirm I've been on the inside.  Its not pleasant and it isn't always on purpose, but it happens.  The things you really want to avoid in big convection are the updraft and near the updraft where the big hail is falling, while keeping in mind small hail can be lofted in the anvil.

Cumulus clouds are much lower than the cruising altitude of airliners. You'll never encounter a cumulus in level flight with an airliner.

@vsz: Cumulus clouds probably not, but cumulonimbus clouds often extend well above 40,000 ft. And when there is a squall line across your path, you use the radar to avoid the worst parts but there is some turbulence wherever you fly.

I have literally had to deviate off course because the heads of cumulonimbus clouds were towering above our service ceiling of 40k.

TL;DR clouds and a Doppler radar in the nose registering uneven air.
If the plane flies into clouds then there will get some turbulence because at the boundary the air will change, especially in thunderclouds.
Clear air turbulence is more devious as it happen in clear air (like it says in the name), these are detected by instruments on the plane like a Doppler radar that can detect the uneven air ahead.
Besides those methods, planes ahead of them will be able to report that they experiences turbulence so the pilots behind them can anticipate.

Note that radar can only see things like rain, hail, bugs and birds. Radar wont show you clouds or clear air turbulence.

Yeah, casey is correct. Radar doesn't show CAT. You just have to get reports from other pilots for that.

At night time and with a broken radar....
The above mentioned methods are good but the ability to plan ahead and perhaps even give you that brief whilst we are on the ground is due to the fact that we always carry the latest Significant Weather (SIGWX) charts that cover our route.
Here's what one looks like (view in new tab):

You can find a legend for such a chart online but basically the thick bold lines indicate strong upper level winds (also known as jet streams). Crossing one of these at right angles is what brings the most amount of turbulence.
Second to that, the areas contained within the cloudy bubble like shapes (making it very easy for you to understand here ;) ) are areas in which we can expect to find CB clouds or other storm related activity. Of course, flying through a big lumpy CB cloud will almost always have turbulence associated with it. ISOL EMBD means the CB clouds are isolated (relatively speaking few and far in between) and may also be embedded inside other types of clouds that are in that area. Most of the time and especially in winter we fly above these areas anyway (for cruise at least).

Does the volcano signs mean that those volcanoes are expected to be active?

Pireps is how I get most of my info. And you should pass them along on handoffs between controllers.  When I get a handoff I say something like "Denver Center, N12345, level 250, light chop".  They will respond back with "N12345, Denver Center, it should smooth out in 50 miles or so".

According to the FAA the official Way is still ask a Flight Service Specialists in preflight briefing who the weather forecasts are and if turbulence can occur.
But additional in the preflight briefing the Pilots can see like on this Site the turbulences.
It is also stated in this FAA Document:

For pilot reports (PIREPs), the
  ADDS Java tool can zoom in on a
  specific part of the country and
  specify the type of hazard reported
  (icing, turbulence, sky and
  weather). The tool also allows you
  to limit data to specified altitudes
  and time periods. Map overlays
  including counties, highways,
  VORs, and Air Route Traffic Control
  Boundaries are available.

Is there any pilots typed rated on 707 who can answer the following;in Aug 1989 I was travelling aboard a domestic flight on a PIA 707-320_

C. I was travelling on a domestic flight from Karachi to Lahore. During the flight the aircraft started to drop while level with engines roaring . The aircraft seemed in a downward wash looking outside it was pitch dark . I was so alarmed that me my mother uncle and aunti started to hold each others hands. The aircraft then settled off and calm fell to me that my prayers were answered. It there any ex707 pilots or flight engineers out there who can explain to me what this was?

there had been no landing instructions by the cabin crew and can't remember the seat belt indications lights coming on

On my return flight in Nov 1989 from Lahore to Karachi I travelled on a PIA A300B4 without any Scarry momments

I was travelling back home to London were I live.

The most common means in level flight is actually the least technological: pilots ahead of them report the turbulence in that area.
If you are listening to the pilot chatter, and you hear "there is light chop", you can guess that the seatbelt light is about to come on.
(This is an interesting answer to a related question illustrating this point - the pilot refers to "ride reports" and PIREPS.)
Generally, if weather conditions are bad enough to show up on radar, you don't fly into them at all.
It's true that flying into clouds is another time when they know there will be turbulence, but this is most often on ascent or descent, and seatbelts will be on anyhow.


text:
How do engine manufacturers derive varying amounts of thrust from a single engine model?
What changes do manufacturers make to an engine to vary the amount of thrust it produces for different applications? Take the GE CF34 for example where there is a 10780lb difference between the thrust produced by the smallest CF34-3 and CF34-10E.

@Penguin we do not allow answers in comments Please feel free to post an answer.

The CF34-3and CF34-10E are quite different engines. The -10 produces more thrust for a number of reasons:
It has a higher mass flow. The CF34-3 has a 44 inch fan, while the -10E has a 54 inch fan. So, the mass flow will be higher in the -10E, and thrust is related to mass flow.
The bypass ratio is different, the -3 is 6.2 while the -10E is 5.4.  This is also due to the different fan diameters, and will cause a difference in thrust (even if the mass flow was the same.)
They are significantly different engines. The -3 weighs 700kg, while the -10E weighs 1700 kg. So, it's a lot more than just a tweak of the blades, or a change in fuel scheduling, neither of which will change the weight. With such a weight difference, you would actually expect the -10E to be about twice as powerful, so a question would actually exist if it wasn't considerably higher than the -3.
The turbine temperatures are also different, due to the large difference in technology levels of each engine. The -3 was certified in 1995, in comparison to the -10E in 2013.The EASA type certificate EASA for the -10E shows the max allowed EGT at takeoff is 983 Celsius. The -3 max EGT for takeoff is only 871 Celsius, in comparison.
With regards to overhaul intervals, this info is generally proprietary, as it's commercially sensitive. So, you won't find much info. Suffice to say, airlines don't make money if the engines need to be overhauled often, so later versions with better high temperature material capability are likely to have longer overhaul intervals, than earlier generation engines made in a time when shorter periods was the norm, and acceptable then, but not now.

When originally developed, an engine design will have a "thermodynamic limit" that sets the maximum energy you can pull out of the basic core configuration.  Because the initial development is super conservative, when first developed there will be ample thermodynamic margin in the design, allowing more energy to be passed through it with various detail changes and improvements on subsequent versions, as the design is proven in service.  For example, compressor blade improvements or the addition of compressor stages will allow you to dump more fuel into the burner can, letting you drive a bigger fan and increase the thrust rating.
There are negative side effects.  At some point as you pull more and more power you start to bump up against the physical limits of the core and as you do, you start significantly eating into the engine's service temperature margins (the difference between the normal operating ITT and the maximum ITT among other things), to get the thrust ratings you want, which means lower and lower time between overhauls.
The -3 versions of the CF-34 are quite under stressed and these run quite a long time between overhauls.  As you move up the dash numbers the average hours between overhauls gets shorter and shorter.
On the CF34 particularly, there is a another major difference between the -3s and later ones, because the compressor inlet behind the fan is "flush" to the inner cone of the fan's exhaust duct to make the engine more FOD resistant (a goal of the A-10 program where the engine was originally born).  On later dash numbers, to improve the windmilling ability and operating efficiency, GE altered the compressor inlet to get a bit more ram effect.  This had the side effect of engine pulling in a lot more grit, which erodes the compressor blades a lot faster and shortens engine life (using flex thrust helps with this a lot).


text:
What do these white on red words indicate on a London Heathrow taxiway chart?
What do the words in white block capital letters over a red background denote on this aerodrome chart of LHR?

Could you source the image, please ?

@kebs http://www.ead.eurocontrol.int/eadbasic/pamslight-A22138EF822CCA53AD188B9B368A7757/7FE5QZZF3FXUS/EN/Charts/AD/AIRAC/EG_AD_2_EGLL_2-1_en_2018-12-06.pdf

They are named holding points; this allows them to say things like "taxi to RABIT" rather than "taxiway Bravo, hold short of taxiway Charlie". This saves a lot of time for ground controllers at busy, complicated airports.

Might be worth mentioning how these unusual names were chosen; https://www.flyertalk.com/forum/british-airways-executive-club/1536531-ask-staffer-7.html

Thanks for that @Richard !  Intriguing they are FIVE LETTERS only.

@Fattie The reporting points or intersections in the air are five letters as well.

It's the name of the holding points if ATC asks the plane to stop in the middle of the taxiway to avoid collisions

authors: Vladimir F Героям слава


text:
In the UK, which ATS unit would be responsible for CTR entry clearances?
In the UK, which ATS unit would be responsible for CTR entry clearances? Would the approach controller issue them, or would the approach controller need to co-ordinate a clearance from the aerodrome controller? If the former, I assume the approach controller would pre-note the aerodrome controller?

Are you talking about IFR or VFR? For IFR flights the clearances are usually given by clearance delivery before departure.

Sorry should have specified, I'm referring to VFR.

The answer depends on which aerodrome you are talking about, and can be found in the UK AIP: http://www.nats-uk.ead-it.com/public/index.php%3Foption=com_content&task=blogcategory&id=165&Itemid=3.html
Click eAIP to open the electronic AIP. In the left menu, open the AD 2 Aerodromes section and navigate to the aerodrome in question. Then open the AD 2.17 section of that aerodrome.
In AD 2.17, airspaces related to the specific aerodrome are listed. Column 1 contains the airspace designator and lateral limits. Column 4 contains the responsible ATS unit.
As an example - the Birmingham (EGBB) CTR is controlled by Birmingham Approach.


text:
Which airports in Ireland use Surface Movement Radar?
I know that Dublin uses SMR, but do any other airports in Ireland use it?

The wording of this IAA information implies that it's Dublin only:

The IAA also operate an Advanced Surface Movement Guidance and Control
  System (ASMGCS), which facilitates the safe movement of aircraft and
  airport vehicles at Dublin Airport, even during poor visibility
  conditions. The ASMGCS incorporates Surface Movement Radar,
  Multilateration and ADS-B.

There's a similar comment in this document. And the AIP entry for Dublin mentions surface radar in the obstacles list, but the entries for Cork and Shannon (the next busiest airports) don't.


text:
What is situational awareness and why is it important?
What is the definition of situational awareness? In which phase of flight is situational awareness the lowest, and why?

A simple definition of situational awareness that you are aware of the different situation happening around you, know why they are happening and can think of an action you need to take to tackle with those.
In aviation, situational awareness means:

For a pilot, situational awareness means having a mental picture of
  the existing inter-relationship of location, flight conditions,
  configuration and energy state of your aircraft as well as any other
  factors that could be about to affect its safety such as proximate
  terrain, obstructions, airspace reservations and weather systems. The
  potential consequences of inadequate situational awareness include
  CFIT, loss of control, airspace infringement, loss of separation, or
  an encounter with wake vortex turbulence, severe air turbulence, heavy
  icing or unexpectedly strong head winds.

As far as your second question, hypothetically speaking, one can say that going through the preflight checklist, pilots are more focused inside the cockpit mostly and the situation outside the airplane is not too much of concern until they pay attention to that.
Generally speaking, when the airplane is not moving, situational awareness can be lesser. It is same as when you are driving, at what time you have lesser situational awareness?


text:
What's the difference between "dumping" and "jettisoning" fuel?
There are some countries (Sweden, for example), they do not permit "dumping" fuel, only "jettisoning" procedures.
Is there any difference according to the amount of fuel that will reach the ground? And the area surrounded by the fuel released?

Related, maybe a partial dupe?

OP do you have two accounts? The suggested dupe was asked by someone with the same, uncommon, name as you. I think the previous question should be edited to ask if there are regulatory definitions/differences.

OP, if you want to regain access to your old account(s), follow the procedure here: https://aviation.stackexchange.com/help/merging-accounts


text:
What is the difference between "amended" and "revised" clearances?
Reading the ICAO Phraseology Reference Guide I saw the term amendment applied to clearances, and I got a bit confused about how to differentiate it from a revised clearance. What does each one mean? Are there any examples?

In the US, I routinely hear "Callsign 11, I have an amendment to your clearance, advise ready to copy" and also "Callsign 11, revised clearance, advise ready to copy."  There is no practical difference that I'm aware of -- in both cases they're giving you a new clearance. There may be some term of art for the controller, but for the pilot it's same-same.  Can you link to where you're seeing the two terms used in ways that seem to imply a difference between them?

(http://www.pprune.org/airlines-airports-routes/165139-revised-departure-clearance.html) revised clearance

(http://www.skybrary.aero/bookshelf/books/115.pdf) amendment clearance

ICAO Doc 9432 mentions the phrase RECLEARED, which means: "A change has been made to your last clearance and this new clearance supersedes your previous clearance or part thereof." Which exact document have you found a reference to amendment in? I can't find it in doc 9432

An amended clearance usually indicates something has been added to it, but the original content remains the same. Revised usually means the clearance has had modifications to the original content, including possible additions and deletions.

please consider registering an account, instead of creating a new one for each post

Please add the source for this information to add credibility to your answer.


text:
Self-flying commercial aircraft!
I'm sure that all the technological advancements in various field are enabling us to create or develop stuffs which were unthinkable even few decade ago. My question is what is the current R&D stage in self flying commercial aircraft or any project in the pipeline ? Also, who is leading this concept?

We don't have the self driving bike anymore, it was only available on April 1st .

Self-flying is not enough. There are self-flying aircraft, e.g. drones. There are self-flying airliners, e.g. on autopilot. So the question is the degree of autonomy, which cannot be total: there are tasks still requiring a human, e.g. deciding when the aircraft flies and where it goes, and it's easy to think about more tasks like that.


text:
What is the US FAA concerned about when it comes to psychiatric medications?
I don't understand the FAA's policy for psychiatric medications (specifically anti-depressants). Obviously I'm glad there is oversight into who can obtain a pilot's license for the safety of the pilot, crew, passengers, and the people on the ground. And obviously people need to be in a stable condition before they eligible to fly. But some of these rules sound ridiculous to me.
First, they won't approve you to fly while taking a psychiatric medication, but they may approve you to fly if you decide to go off of it for 60 days.
What?
So basically if you have a chronic mental health condition, and you are taking a medication for it, and it's working well without side effects, it's better to go off the medication before you try flying? Wouldn't the disease be more apt to return if you were off the medication, than on it? That sounds like a very stupid risk for the FAA to take.
Are they worried about side-effects? Most of the side effects for modern SSRIs are very limited and/or transient and/or don't apply to flying (like constipation), so I know they can't be worried about those.
Are they just concerned about withdrawals if you miss a dose? That seems pretty unlikely to happen, and probably less likely to cause trouble than to go off meds entirely.
Basically, I don't get it. It seems that if you are fully-treated for a condition without side effects that you should be eligible to fly, regardless of whatever drugs are put in your body. Honestly, I'd be more concerned if people were taking less medications for passing a test, than what they were on before.

Note that both the anti-depressant medications and the underlying mental illnesses they are meant to treat are disqualifying conditions.  So going off medication for 60 days won't lead to an approval if the condition it was treating persists.

Not familiar with the US way of doing things, but this sounds like you can get a 'special issuance' certificate on anti-depressants: "For a minimum of 6 continuous months prior, the applicant has been clinically stable as well as on a stable dose of medication without any aeromedically significant side effects and/or an increase in symptoms"

@BigEndian My point was that even if the condition doesn't persist after 60 days (on medication or not), if it's likely to return at all, it's more likely to return while you're not on medication. Seems like you'd want to error on the side of medication.

@Jason And your point is well taken.  I agree with your logic.  But the FAA does not.  See my answer for my best guess as to why.

I think that the medication rules were created at a time when psychotropic meds were not very common and were mostly used for people with more serious diagnoses, such as bipolar and schizophrenia. Those old meds also had a lot of side effects. The use of newer meds to treat milder conditions has only really been around since the 1990's and the FAA is moving very slow in figuring out how to integrate it safely into the rules. Now that so many people take them they have started to loosen up a bit, approving 6 ssri's for special issuance and sometimes adhd meds.

The FAA is concerned that individuals taking anti-depressant medication will not have the mental focus required when juggling multiple tasks in real time in the cockpit.
anti-depressant medications are psychotropic -- They are specifically intended to alter the takers' mental state.  The assumption is that any artificial modification of mental state will negatively impact aeronautical decision making.
The SSRI special issuance protocol requires, among other things, the applicant to demonstrate the ability to quickly and accurately perform multiple tasks simultaneously.  The idea is to make sure that you aren't being slowed down by the medications to the point where you can't make the right decisions rapidly enough to ensure safety of flight.


text:
When (if ever) can ATC order an aircraft to go around?
Can ATC order an aircraft to go around if there is a tailwind? Or should ATC give the pilots the current wind information and let them decide whether to go around or land?

Most commonly it's because the aircraft in front of you didn't get off the runway fast enough.

In real world practice, ATC will have a specific direction for traffic to land and takeoff based on their specific criteria. Regardless of which direction ATC chooses to make the traffic flow, the PIC can choose any runway and/or direction he wishes to land. As long as both parties coordinate and agree, the aircraft can land based on the ATC’s chosen direction or the pilot’s chosen direction. ATC will usually make sure approaching aircraft are kept aware of the wind conditions so that agreement can be made. Either party can decline/deny the approach and/or landing.
An example of this is when aircraft approach our local Class D airfield VFR. They announce that they are inbound with the intention of landing. The PIC will typically then accept whichever runway ATC assigns. When an aircraft approaches IFR, they will typically know which approach and runway they wish to use. The PIC will typically have already negotiated/coordinated this with approach before being transferred to tower. If the aircraft is approaching the airport practicing IFR in VMC, they will negotiate/coordinate the approach and runway to use directly with the tower.
ATC is responsible for traffic separation in their area of jurisdiction. Although, the PIC has ultimate authority over the safety of flight of his/her aircraft, ATC has the authority on whether that flight can include ATC’s physical domain. That domain includes specifically the runway and taxiway surfaces. They can choose whether or not to give an aircraft clearance to use the runway. They can also revoke that clearance for the sake of safety. Some instances where ATC may revoke clearance and call for a go around include:

Reversal of surface winds.
Windshear.
Runway incursion by another airplane.
Runway incursion by a ground vehicle or personnel.
Runway incursion by an animal.
Ceilings or visibility going below acceptable runway visual range.
Closing the airfield due to an accident or emergency.
Inadequate spacing between aircraft.
Landing gear issues unnoticed by the landing pilot.
other safety issues specific to ground or airfield environment safety.

Even before an aircraft approaches the airport for landing, ATC can prohibit them from entering their airspace in its entirety. The aircraft will have to remain outside of the airspace until ATC gives them the clearance to enter.
All of this can be superseded by the PIC in the case of an actual emergency on the part of the aircraft.

Thank you for that perfect answer

@Vito - Thanks for the compliment. I’m sure someone else could have given a more complete yet briefer answer. There are a lot of smart people on this site willing to help and answer questions.

It's important to note that aircraft are often certified to a specific tailwind component for takeoff and landing, typically 10 kts or 15 kts on jets, 5 kts on light aircraft.  That's component, not a direct wind speed limit, so a 20kt quartering-from-behind crosswind that imposes a tail component of 10kt is technically within the airplane's operating limitations if it's certified for a 10kt tail component. The controller can't know what applies to a given airplane and therefore generally won't try to make those kinds of judgement calls, that are really airmanship, except in extreme cases.

@JohnK They can offer not-so-subtle hints, though. From my student days: “Cessna 123AB, runway 36, cleared for the option. Wind. One. Eight. Zero. At. One. Zero.” That made pattern work a lot more interesting!

Generally speaking, ATC must instruct an aircraft to go around whenever the controller has reason to believe the landing cannot be performed safely. In most cases, an ATC-initiated go around is caused by unexpected unavailability of the landing runway, for example if another aircraft, vehicle, person, wildlife (birds) or obstruction enters (or fails to leave in time) the runway.
The controller does not know the limitations of every  specific aircraft type. Factors such as wind (crosswind, tailwind), braking action (snow/ice on runway) and ceiling/visibility is announced to the pilot, who is responsible for ensuring that the prevailing conditions are within aircraft and crew limitations. Crucially, different aircraft have vastly different limits, and they can even change from flight to flight (maybe one day the aircraft is heavily loaded and need a longer runway, for example.) The pilot knows the specific limitations, the controller does not. So a sudden change in wind should not cause the controller to instruct the aircraft to go around, rather, the controller will inform the pilot of the change, and it is up to them to determine whether or not to continue the approach.

Both answers are correct, just want to add my perspective here.
ATC can definitely tell an aircraft to go around. It happens all the time at busier airports. Almost 100% of the time it will be so that we as controllers maintain legal separation: the previous plane took too long on the runway, you're closing too fast on the plane ahead of you short final, there was a runway incursion, etc.
I can only think of a couple of instances where I would tell a pilot to go around for a non-traffic related reason: Landing gear appears up, aircraft appears lined up with a taxiway or incorrect runway, or aircraft is inside the final approach fix on an instrument approach and is obviously off centerline. That's about it.
All the rest of it—tailwind, wind shear, even low visibility or RVR—is not my area of expertise. You're the PIC. If you want to land with a 30-knot tailwind that's on you. If you want to land when the ceiling is showing VV001 that's on you. My job is to give you the information I have and let you decide if your skills, your aircraft's performance and configuration, and the FARs allow you to continue.


text:
Will air accelerate over a wing and generate lift, if the air has zero viscosity?
Will air accelerate over a wing, if the air has zero viscosity?
Will the wing produce any lift under these conditions?

This is a great question.
When there is lift, there is drag. Can there be lift without drag?
Air with zero viscosity would have no friction, and thus there would be no air resistance and no drag.
I don't think you would be able to fly.
I'm gonna ask my aerodynamics and physics teacher to give him a real mind-bender.

@mins Huh, that's neat, i'm gonna be reading up some more on this! Thank you, very interesting!

@mins that page seems to assume the flow field will still look the same without viscosity, but it will not.

This question was closed as being already asked and and answered elsewhere. Really the other question is not about viscosity and the selected answer doesn't even mention it. Of course the boundary layer is linked to viscosity, but the question asks for a better level of explanation. Voting to reopen. (As a side comment, duplicates are not to be evaluated by their answers but by the question itself. It not because some answers in the other page mentions viscosity that the question itself is the same.)

TL;DR: Inviscid flow is not physical, however theoretical inviscid flow can still flow around a streamlined body (such as a wing) and it will produce lift.
There is no such thing as zero viscosity, so all we can use to answer your question is theory.
In the theory, there is "inviscid flow", and it's an extremely useful tool we very commonly use to explore preliminary designs, especially high Reynolds number flows where the viscous effects are far outweighed by the inertial effects. Essentially inviscid flow isn't some special case, it is just flow with an infinite Reynolds number. If you increase Reynolds number further and further, the flowfield changes less and less. It is not crazy to think that this converges are Re approaches infinity.
Before CFD and all the complicated ways of modelling fluids existed, physicists used Potential flow to model theoretical flow. Potential flow follows all the same behaviour as real flow, except it does not account for viscosity. It's impressive how many geometries were modelled by combining sources, sinks, vortices, and doublets. One of the simplest and most famous examples is the Zhukovski/Joukowsky (depending on your textbook!) airfoil, which is a simple doubled (source + sink) with a vortex. The vortex induces circulation in the fluid and gives the airfoil it's cambered shape. Because the vortex induces circulation in the fluid, it generates lift (Kutta-Joukowski Theorem).
The common misconception is there has to be some viscosity to "hold" the fluid together or "stick" it to the surface. In fact, the opposite is true: the fluid cannot detach from the surface because there is nothing to fill in the void. This can easily be seen when using an inviscid flow solver such as JavaFoil - try increasing the angle of attack more and more, and the flow never separates.
Even very sharp corners will keep attached (unless the Kutta condition is explicitly applied). The force required to turn the flow around a sharp corner is "reacted" by the force felt by the surface that is turning the flow, the flow direction bends towards the surface, and the surface feels an upwards pressure - essentially Newton's Third Law. This pressure reduces further away from the wall, and so does the amount of turning on the flow. This should hopefully explain how flow can remain attached to a surface as it bends away from the flow.
When modelling inviscid flow, you must be careful not to take the results as physical. Seperation will never be predicted, even with add-on Boundary Layer models.
Hopefully this makes enough sense, but please feel free to ask for clarification on anything.

Thanks @mins. What do you think needs elaboration? Yes there will be flow across the wing, and that will produce a pressure difference (plus acceleration/deceleration) and therefore a lifting force. I'm happy to provide further details where you think.

Stuart, actually when I read again your answer I find it talks about everything needed, for some reason I misread it the first time and focused on the KJ solver part, but I see you talk about viscosity not required to maintain the flow against the airfoil, which is I think the main point of controversy, and you also emphasized that it's a misconception. The only thing to add, would be a superfluid airfoil experiment, but I guess that will be difficult! So +1, and more if I could, and I apologize for the first comment. I hope the question will be re-opened.

Finally I found something related to lift in superfluid which contradicts the original thesis of  non-lifting superfluid helium.

@mins glad you found it useful - I'm always happy to try and communicate clearer. That paper you found is fascinating. Very interesting that they use the Zhukovski airfoil so as to get a direct comparison with the closed form potential flow solution. Thank you for sharing it!

Awesome paper! Question though, doesn't the kutta joukowski theorem only concern 2D potential flow? There's a great leap between 2D flow and 3D flow. I feel like the answer to this question is very double sided.

@Noddle, the concept of circulation and the Kutta-Joukowski theorem absolutely apply to 3D flow. If you look at lifting-line theory, the idea is to calculate the lift distribution over a wing by relating the circulation (you can think of as vorticity in the airfoil crossection) to shedding vorticity from the trailing edge (in the plane perpendicular to the flow direction).

TLDR: No viscosity -> no friction, no friction -> no boundary layer, and no boundary layer -> no pressure difference, no pressure difference -> no lift.
Difficult question to answer, took a lot of reading up
Let's start here though, an excerpt from some NASA educational material.

Aerodynamic forces depend in a complex way on the viscosity of the gas. As an object moves through a gas, the gas molecules stick to the surface. This creates a layer of air near the surface, called a boundary layer, which, in effect, changes the shape of the object. The flow of gas reacts to the edge of the boundary layer as if it was the physical surface of the object.
(grc.nasa.gov)

The viscosity - its friction, stickiness, and compressibility, is what gives us the boundary layer on our airfoil.
ok
If we dive deep into the lift and drag, we will at some point meet viscosity with the Reynolds number.
Reynolds number is defined as
$$ \text{Re} = \frac{r \times V \times L}{\mu} $$
Where $\mu$ is the viscosity of our gas.
First of all, with a viscosity of 0, our equation would fail us already since you can't divide with 0.
We'll just go ahead and say our viscosity is really small then.
Dividing anything with a really small number, will give us a really big number as a result.
I found this to describe what happens aerodynamically with really high Reynolds numbers:

Image from (eng.cam.ac.uk)
If we take a look at 8.5, we see that our boundary layer becomes turbulent before the equator, and we don't see flow separation until we reach the back side of the ball.
This is with a Reynolds number at 200000 (so there's still some viscosity)
This looks great for our theory of lift without viscous air! higher Reynolds number = less drag!
While this is true, it doesn't necessarily mean our lift is getting any better because of this reduced drag.

The problem we run into, is pressure.
We need pressure to build lift. If there is no friction, our air molecules won't stay around long enough for us to build pressure.
With no viscosity, we have no friction, and with no friction, we have no boundary layer, and no pressure buildup.
What generates lift (according to Bernoulli) is the difference in pressure over the wing, compared to under the wing.
With no friction, we won't be able to achieve this.
There is no lift without viscosity
Extra
Just after finishing this answer, i found this paper (researchgate.net) Titled: the Explicit Role of Viscosity in Generating Lift. In their conclusion they state:

The formal expression for the fluid-mechanical force (or aerodynamic force) of a body in an incompressible viscous flow is given, which explicitly elucidates the critical role of the fluid viscosity in generating the force (the lift particularly)

and

the vortex lift is evaluated as the consequence of the viscous boundary layer

I will gladly try to answer any follow-up questions and critiques!

Thank you for all the quick edits @Bianfable ! :) A nice way for me to learn the formatting!

No problem ;) If you need more info on MathJax, here is a good tutorial and quick reference on Mathematics.SE.

So in potential flow, which assumes an inviscid fluid, lift is impossible? That is not in agreement with a lot of well established software.

@PeterKämpf I am gonna refer you to the top answer in this physics stack by tpg2114, its introduction and conclusion. https://physics.stackexchange.com/questions/46131/does-a-wing-in-a-potential-flow-have-lift/46134#46134
And to quote Vladimir F from the comments:
The overall answer is, no, it does not. Or it does not have to. Unless you introduce the circulation by some additional means and then it can have any lift depending on the amount of circulation introduced.  "no viscosity" is an artificial thing, but so is irotational potential flow.

@PeterKämpf, doesn't all that software enforce the trailing stagnation point to the trailing edge (which is the one thing that wouldn't be defined without viscosity)?

The boundary layer is slower than the free stream, but to reduce the pressure above the wing the flow needs to be faster, so the argument about needing the boundary layer for that does not stand on its own. My understanding is rather that viscosity is essential for making the fluid follow the wing instead of some vortex filling in (and stall occurs when it is no longer sufficient to do it).

@JanHudec I agree, the viscosity is what makes the fluid follow the wing. It's what keeps the boundary layer sticking to the airfoil.
And you're right, faster flow = lower pressure. There will inevitably be faster air molecules over the top of the wing. but because there is no viscosity, no friction, the air that's moving fast won't accelerate air above it. Thus the reduction in pressure would be negligible.

If you want, i can make some images tomorrow, to clarify my meaning. My mind goes straight to the boundary layer velocity profile, but somehow with no friction.
It would almost be opposite

The argument that you cannot generate a pressure difference without a boundary layer doesn't make much sense. Unfortunately as with most theoretical aerodynamics, there is not a simple cause & effect relationship - flow stays attached because there is circulation induced by the shape of the airfoil and a pressure field that causes the flow to bend around the airfoil. None of this can be seperated from the other, these are all just human invented ways of explaining something very complex.

The argument from no friction to no acceleration of the air is exactly the one that is contradicted by most of the CFD software neglecting viscosity in the stream. The only point where viscosity has to be taken into account is around the trailing edge (which a lot of the software simplifies to enforcing additional boundary condition).

@JanHudec That is exactly right. The Kutta condition needs to be enforced to get the correct lift. However, of all rear stagnation point positions there is only a single one which does not involve lift. All others produce some lift, albeit one that does not fit to viscous reality.

@mins has provided a fascinating paper in the comment below. It directly addresses the Kutta condition assumption in inviscid flow (Introduction - Paragraph 2).


text:
Is this vintage altimeter from the Cuatro Vientos?

My father who was a pilot, passed away some years ago and I have a vintage altimeter that he told me someone gave him.  They assured him that it belonged to the Cuatro Vientos airplane, but I'm not sure if this is the case. I've seen some pictures from the Cuatro Vientos's cockpit, and this instrument isn't very similar to the instruments in the photos I've seen. However, the painted text reads "Altura kilómetros", instead of "Altimeter". The text below that reads

Pioneer Instrument Company
Brooklyn New York
199-2044

I hope someone can help me find out if it was from that airplane. (Sorry for my English; I'm writing from Mexico City.)
Thanks in advance.
-Miguel Anaya

It may help if you provided a picture or two of your altimeter. [Edit] your post, then either click the "sun and mountain" icon above the text entry box and browse to the pic, or, just drag the pic into the text edit box. The SE servers will upload & host the image for you.

Welcome to the site. Your question isn't clear, what is it you want to know? Bring some light about it is very broad.

We may be able to rule it out, but if it is at all similar, knowing if that exact altimeter was in that aircraft may be at best very difficult (without examining records showing serial numbers)

According to the Wikipedia article you link to, the aircraft disappeared without trace. It would seem unlikely, then, that this could be something from that aeroplane.

It could have installed and then removed sometime during the 4 years it operated before it disappeared.

The wreckage of the 'Cuatro Vientos' was found in 1996. The crew had been apparently robbed, killed and partially eaten up by the savage natives...  https://www.abc.es/archivo/periodicos/abc-madrid-19960312-75.html

The plane was a Bréguet 19. This is a photo of the instruments panel of a similar aicraft (Point d'Interrogation used by Costes and Bellonte). This give an idea, but not sure two of these planes had the same panel.


text:
Do the different spoilers on an A321 extend by different amounts?
I recently flew with an A321 and watched the left wing while the pilot tested the control surfaces before lift off. I noticed that one of the spoilers angled upwards much less than all others. In the drawing below, it was spoiler number 3 (labelled as an "air brake" [sic]). The pilot extended them twice, and the behaviour was the same each time.

The answer for "do they do X" is certainly provided when the answer to "why do they do X" confirms that X happens as introduction to explaining why. I see no value in reopening, particularly since the OP found the duplicate thread to be useful.


text:
How far away should the vertical stabilizer be from the leading edge of the main wings?
I am wondering what the advantages and disadvantages are of placing the vertical tail nearer to, or farther from, the main wing. For instance, when the vertical tail is just behind the wing, do the wing's effects on the airflow around the aircraft decrease the effectiveness of the vertical tail?

Some aircraft don't have a tail (I presume you mean a vertical stabilizer) at all. Please [edit] your post to clarify what you're after. After all, entire books have been written on aircraft design.

It should be about seven feet away from the trailing edge of the main wing.

The reference point is not the leading edge but the center of gravity (CG), which is a little further back.
The ability of a fin to generate a yawing moment is proportional to both its area $A$ and its distance $l$ behind the CG. It is therefore also proportional to their product. This has units of $L^3$ so it is known as the tail volume $V$:
$V = A.l$
So the nearer the fin is to the CG, the larger it needs to be. On the other hand, the smaller a fin is, the farther back you have to build it out.
In practice everything in front of the fin, usually the fuselage and/or wing, can affect the airflow over it and reduce its effectiveness. This is especially significant at high angles of attack, such as when taking off or landing, and extra height is often added for this reason.
However a very tall fin also exerts a strong rolling moment, which can cause awkward stability problems such as Dutch roll.
At supersonic speeds, the pressure above the rear of the wing and fuselage falls, reducing the effectiveness of the fin. However the pressure under them increases, so underside strakes become very effective for their size.
Placing a very large fin above and close to the main wing is about the worst thing you can possibly do.
The optimal distance back depends on many design factors but is usually around a half- to three-quarter span, though it can be further for supersonic aircraft.

I've always wondered how the F-18 got away with having the V fins so far forward.

The F-18's fins are relatively large for a twin-fin aircraft; they are approaching those of the F-14 on a machine little more than half the size and weight.

Compare the B747-200 and the B747SP.  The shorter SP had a much larger vertical stab.

The answer depends on many factors. The most important one: What is the vertical tail needed for? This will be a combination of several functions, and the most pressing need will determine its size and location:

Counteract asymmetric thrust in multi-engined airplanes. With all engines running, the B-52 is still flyable with almost all of its vertical gone.
Provide yaw damping. For GA aircraft, the yaw oscillation has to die down to a tenth of its original magnitude after no more than seven cycles. Since damping grows with the square of the tail's distance to the center of gravity while control power only grows linearly, you should shift the tail further back if you need more damping.
Get the airplane out of a spin. Here it is important to have some part of the vertical exposed to the airflow even at very high angle of attack. This means that the vertical tail should be placed a bit ahead of the horizontal tail, or a T-tail is used.
Counteract adverse yaw: Here the wing's aspect ratio dictates how far the vertical should be shifted back. More slender wings require more distance between center of gravity and the vertical tail.

As you can see, the location relative to the wing's leading edge is not important. Measure the distance to the center of gravity and let it grow with wing span. Start with 40% of span (for gliders maybe 30% of span), size it for control power and increase the distance if damping is insufficient. Add some margin for wing-mounted engines.


text:
What is the approximate price of a McDonnell Douglas MD-80 series aircraft?
Does anyone know the approximate price of an MD-83/87 aircraft manufactured between 1990 and 2000?

You're looking for purchase price only, not concerned about operating or maintenance costs, or repairs likely to be needed on a 20-30 year old airframe (probably including new/rebuilt engines if the airframe has been standing in a boneyard)?

Prices on any aircraft can vary widely based on hours, configuration, included documentation, service history, and even current location. Can you provide us some more parameters?

Looking at the edit history, I'm not sure why this was closed with "needs focus" as the reason. There's only one question. It may still be off topic, as a price request, but not because there are too many questions. Or am I missing something?


text:
Can/do commercial flights change their flight path during flight?
Looking at the paths of the same flight on two different days, I noticed they flew very different paths.
Short Path:1
YAY N184B TOPPS ENE PARCH1

Long Path:1
NIBAX G462 TUMAK UL602 ORSOL UL602 DAVUS UL602 TASMI UL602 ITBIT UM860 KABAN UT334
INB UL852 UDROS L621 REVDA UP193 CND UP193 KARIL UL624 LABUK UY444 ELMEK UL726 OKG
UL984 NOSPA TOLVU UN857 GIMER UT300 EVX UT176 LGL UN491 KOKOS UN585 REGHI UN480
ETIKI NATD DOVEY LACKS BERGH L454 OWENZ CAMRN CAMRN4

I asked a similar question in the past. This is what I want to know:

What are the reasons which can cause a commercial flight to change its path mid-route?
How it is planed and executed?
I am sure the captain is the final authority on this, but who else is informed?

1Route Source: FlightAware.
P.S.: I could not understand the routes at all.

second final say is ATC, first say is submitting a flight plan

A flight plan is just that, a plan.  A flight can deviate from its cleared route for many reasons, the most common of which are:

Weather
Traffic
Shortcuts

Weather reroutes are often initiated by the crew.

Center, N12345 request 15 right for weather
  N12345 15 right approved for 100 nm, report direct XYZ.

Or they can be initiated by ATC

N12345, Atlanta, your arrival into EWR is in perpetual holding, I can re-route you over PA or NY or do you need to divert? state intentions.

Large scale re-routing for weather will occur when an organized line of convection impacts a major route.  Even a short deviation for weather may result in an amended route if the controller has an alternate clearance he can put you on that works for you (being on a clearance and on-route is slightly less work for a controller than being on a carte-blanche deviation).
Traffic conflicts are usually short term vectors, but if you have an aircraft slowly overtaking you, you may be moved to a parallel route or have you altitude changed.  These, like the weather example above, would result in amended clearances.
Shortcuts are often requested to cut corners or try to make up some time lost in a long taxi on the ground.  These are usually crew initiated, but sometimes ATC will solicit them.  Regardless of what route is submitted in a flight plan, ATC will generally clear you via a preferred routing.  These routes aren't always the shortest distance between a departure and arrival and this is where shortcuts can be requested.  Usually this just means skipping a fix or getting direct routing to a later fix in your clearance.  The availability of shortcuts is a function of traffic, time of day, agreements between ATC sectors, what region you are in and what altitude you are at.
When you are on international flights, another issue you may run into is political and could result in some or all aircraft being routed to avoid certain airspace.
Lastly, your dispatcher may re-route you and ATC will clear you along a new route.

In all cases, whether deviation is pilot or controller initiated, both parties are in sync with what the airplane is doing, which will either be a vector or a new clearance.  Your dispatcher will be notified of this change automatically via their dispatch software (which is likely fed data from both ACARS and the FAA).

Thanks Casey. I didn't completely get about shortcuts concept. If there existed a shortcut which the airplane will take in case of delay in taking off, why they didn't plan it initially? Why they choose to take a longer route when there is a shorter one available?

About changes in path because of political reasons, can they happen on daily basis? Can country X tell country Y "hey, don't fly over us at FL380 tomorrow"? I know about TFRs, but can they affect at that high altitude also?

@Farhan I edited in some more information regarding shortcuts.  In short you can file the shortest route possible, but the ATC computer is going to spit out the route it wants you to fly, not necessarily the one you do.

Can you please explain the political reason too and my question about that? Thanks.

Can 9/11 explain the political reason required re-route?

@Farhan most carriers won't have this problem, but occasionally you hear about a North Korean or Iranian flight suspected of carrying contraband denied overflight by certain countries.  The comment above mine about 9/11 is another example.

Don't forget the Ukraine in the aftermath of MH017.